Japanese Patent Application Laid-open No. Hei8-296455 (laid open in 1996) discloses a conventional technique of a jet engine as one example of conventional gas turbine engines. This conventional technique will be briefly explained hereinbelow.
The jet engine includes a fan which takes in air, a compressor which compresses the air taken by the fan, a combustor which burns fuel in the compressed air compressed by the compressor, and a turbine which is operated by expansion of combustion gas from the combustor and which operates the fan and the compressor in association.
Thus, air is taken in by the operation of the fan, and the air is compressed by the operation of the compressor. When the fuel is burned in the compressed air by the combustor, the combustion gas from the combustor is expanded to operate the turbine, and consequently the fan and the compressor are operated by the turbine. Since this series of operations (operation of the fan, operation of the compressor, combustion by the combustor and operation of the turbine) is continuously carried out, the jet engine can appropriately be operated and a rotational force can be obtained from the turbine and propulsion can be obtained by the combustion gas injected from the turbine.
During the operation of the jet engine, excessive centrifugal force is applied to a rim of a turbine disc of the turbine by high speed rotation of the turbine disc. The turbine disc is heated to a high temperature due to the combustion gas from the combustor and allowable stress of the turbine disc is lowered. Thus, in the jet engine, the following structure is employed to sufficiently lower the temperature of the turbine disc.
That is, the rim of the turbine disc is appropriately formed with a plurality of cooling holes in its circumferential direction, and a portion of the compressed air can flows into each cooling hole as cooling air. A stationary section is provided on a front side and near side of the turbine disc. The stationary section is provided with a cooling duct. The cooling duct is in communication with the cooling holes, and the cooling air is introduced into the cooling holes.
During the operation of the jet engine, the cooling air is introduced into the cooling holes by the cooling duct, and flows into the cooling holes. With this structure, the rim of the turbine disc can be cooled and the allowable stress of the turbine disc can be prevented from being lowered.
In case the jet engine is allowed to operate in a high output state, however, the rotational speed of the turbine disc is increased and a large amount of combustion gas is entrained toward a center of the disc from the rim of the turbine disc. Thus, the flow rate of the cooling air which flows into the cooling passage is increased and it is necessary to sufficiently cool the turbine disc. On the one hand, the turbine disc is sufficiently cooled, however, the consumed flow rate of the cooling air is increased to generate energy loss, and the energy efficiency of the jet engine is deteriorated.
The present invention has been achieved in order to solve the above problem, and it is a first object of the invention to provide a gas turbine engine capable of operating in a high output state by preventing the energy efficiency from being deteriorated.
It is a second object of the invention to provide a gas turbine engine capable of sufficiently preventing the combustion gas from being entrained toward the center of the turbine disc only by flowing the cooling air of small flow rate.